1. Field of Application
The present invention relates to a remote control system for a vehicle, the apparatus including a vehicle-mounted control apparatus which effects control of one or more controlled devices of the vehicle based on wireless communication with one or more portable devices.
2. Description of Related Art
In the prior art, types of remote control system for a vehicle are known whereby, when the vehicle is parked with the doors locked, a vehicle-mounted control apparatus of the remote control system periodically transmits a calling code within a predetermined region around the vehicle, using a wireless communication technology. In the following, the term “radio waves” is used for convenience to refer to wireless communication media in general, such as light waves or radio-frequency electromagnetic waves, and a vehicle which carries a vehicle-mounted control apparatus of a remote control system which is being described will be referred to as the host vehicle. If a portable apparatus which is carried by a user of that vehicle and is configured for wireless communication with the vehicle-mounted control apparatus is located within communication range of the host vehicle, then that portable apparatus transmits predetermined response data upon receiving the calling code. When the response data are received by the vehicle-mounted control apparatus, that apparatus effects control whereby the lock of a door of the vehicle is released, or whereby that lock is set in a stand-by condition whereby it can be manually unlocked. Such a remote control system is sometimes referred to as a “smart entry system”.
With one type of such a system, as described in Japanese Patent No. 2000-104429, the system monitors the calling code and the response data which are exchanged between the vehicle-mounted control apparatus and the portable apparatuses, to ensure that these data will not be improperly used. Specifically, the vehicle-mounted control apparatus transmits the calling code as modulated radio waves in the form of a variable code which is known as a challenge code, and is used as an encoding key. When a portable apparatus assigned to that vehicle receives the challenge code, it encodes the response data by using the challenge code contents as an encoding key, and transmits the resultant encoded response data.
A type of portable apparatus used as described above is generally referred to as an electronic key, and a plurality of individuals may have respective electronic keys that are assigned to the same vehicle. For that reason, with a prior art type of remote control system as described above, when a plurality of individuals are adjacent to a vehicle with each of these individuals carrying an electronic key that is assigned to that vehicle (or an individual who is carrying a plurality of such electronic keys is close to the vehicle), then when these electronic keys respond to the calling code that is transmitted from the vehicle-mounted control apparatus of the remote control system, a plurality of sets of encoded response data will be transmitted concurrently from the respective electronic keys. Hence, the problem arises that the vehicle-mounted control apparatus may be unable to distinguish between the respective sets of response data from the various electronic keys, so that it may become unable to effect the desired control operation, such as unlocking a door.
To try to overcome this problem, a method might be envisaged whereby after the vehicle-mounted control apparatus has completed transmitting the calling code (i.e., which may include a challenge code), it transmits a number of successive bursts of radio waves, with the number of bursts being identical to the total number of electronic keys which are assigned to the vehicle. Each of these electronic keys would be assigned respective burst numbers, and when an electronic key receives a number of successive bursts which reach the number that is assigned to that key, then that electronic key (and only that key) would transmit response data.
With such a remote control system, even if a plurality of the electronic keys were located concurrently in close proximity to the corresponding vehicle, the vehicle-mounted control apparatus would respond only to the response data that are transmitted from a single one of these electronic keys, i.e., the electronic key which is the first to transmit response data after the vehicle-mounted control apparatus has transmitted the calling code. It would appear that such a system would provide reliable communication, even when a plurality of electronic keys are simultaneously located close to the corresponding vehicle.
However with such a system, the individual who carries the electronic key that has been assigned the largest burst number (e.g., when that individual is close to the vehicle and wishes to access the vehicle) must always wait until the vehicle-mounted control apparatus has completed transmitting the maximum number of bursts of radio waves, before being able to access the vehicle. Depending upon the number of electronic keys that are assigned to that vehicle, this may result in a significant delay between the time at which a user approaches the vehicle and the time at which access can be obtained (i.e., a door lock is released or is set in the unlock stand-by condition), which can cause dissatisfaction of the users of such a system. This is a basic problem of such a system.